Lecture by Yaqing Su: Neural Coding of Pitch Cues in the Auditory Midbrain of Awake Rabbits

Pitch is an auditory percept related to the temporal periodicity and spectral content of the sound. Despite extensive psychophysical and physiological studies over decades, neural mechanisms that give rise to pitch perception remain incompletely understood. In the auditory periphery, neurons can convey pitch information via a temporal code to temporal periodicity and a place code to resolved harmonics. In the auditory cortex, a pitch center where single neurons directly represent pitch by their firing rates has been identified in marmoset monkeys. However, how the peripheral representations are transformed into a cortical pitch code is far from clear.

An understanding of such transformation will shed light on the representation and extraction of pitch along the auditory pathway. The goal of the current work is to fill this gap by studying single-neuron response to complex stimuli in the mammalian auditory midbrain. I will first review the current knowledge of peripheral pitch mechanisms, and then introduce the three neural codes we identified in the inferior colliculus of awake rabbits: a rate-place code for resolved harmonics inherited from the periphery, a non-tonotopic rate code for envelope repetition rate that presumably emerges at the midbrain, and a temporal code for envelope repetition rate. I will also discuss the possible mechanisms generating the non-tonotopic rate code. Together, these three codes cover a wide range of frequency, and provide insight for pitch extraction models in higher auditory centers.